In recent years, digital imaging devices using imaging elements such as a CCD and a CMOS remarkably advance, and especially, high resolution, a low cost, and miniaturization are strongly demanded for imaging devices mounted on mobile devices, PCs and the like.
On the other hand, in a high-end imaging device, in order to enhance performance superiority over a decrease in cost, there is a tendency that a size of the imaging element to be mounted is increased.
For example, Patent Document 1 discloses a general configuration in which a conventional large imaging element and a telephoto lens are combined, but a Fno representing brightness of the lens at infinity (the smaller the value, the brighter, and the larger the value, the darker) is about 8, so that the lens is not bright and having poor resolution. In addition, since the telephoto lens has a lens configuration in which four individual lenses are assembled, a mechanism thereof becomes complicated.
Meanwhile, among telephoto lenses compatible with an imaging element having a 645 size having the largest class size in imaging elements for consumer use, the brightest one has a lens configuration of five lens elements in five groups and realizes Fno 3.8 with a focal length of 380 mm (for example, VSD 100F 3.8 of Vixen Co., Ltd.). Hereinafter, this is referred to as a first existing lens.
In addition to the above, there are commercially available lenses compatible with the imaging element of 645 size realizing Fno 4.5 with a focal length of 300 mm with a lens configuration of nine lens elements in six groups as of 2015 (for example, HC 4.5/300 of HASSELBLAD). Hereinafter, this is referred to as a second existing lens.